[tighten] {one's} belt

to lessen the amount of money or resources one uses compared to before, particularly due to having less available

The origin of the idiom "tighten one's belt" can be traced back to the practice of tightening one's belt to make clothing fit more snugly around the waist. This phrase is used to describe the act of reducing spending and living more frugally in response to financial difficulties or a need to save money.

During the recession, many families had to tighten their belts and cut back on unnecessary expenses.
The company experienced a financial setback, and employees were asked to tighten their belts until the situation improved.
The government announced austerity measures, urging citizens to tighten their belts for the nation's economic recovery.
With unexpected medical bills, he realized he needed to tighten his belt and start budgeting more carefully.
With a new baby on the way, they’ve had to tighten their belts and adjust their budget.